We are developing and applying new methodologies to research in epidemiology. This year work has progressed in 6 areas: 1) we have continued work on the problem of how to analyze data that include dependent binary outcomes, such as a rise in reproductive histories; (2) we have investigated the distortions that can be produced by measurement error, even when the error is non-differential with regard to the outcome under study; (3) we have completed work on comparing imputation methods for gaps in exposure histories in retrospective epidemiologic studies; (4) we have continued the development of models for fertility that take into account the timing of intercourse and exposure with potential reproductive toxicity; (5) we have developed a method to identify excess co-incidence of distinct birth defects, important evidence for shared and transient - hence potentially environmental - etiologic factors; and (6) we have developed improved epidemiologic study designs and methods of analysis aimed at characterizing etiologically important interactions between environmental and genetic factors.